At Work: Hiroshi Kawase

1 October 2018–Before becoming a professor within the Sophisticated Earthquake Risk Evaluation Program – part of Kyoto University’s Disaster Prevention Research Institute – Hiroshi Kawase seemed destined to become an architect or structural engineer.

Kawase on the roof of a newly constructed skyscraper in Osaka, Japan

He grew up watching his father design and build houses at the same time Japan was making major investments in infrastructure. In elementary and junior high schools, he was inspired by documentaries on the construction of the Kurobe No. 4 Dam, the Seikan Tunnel and the Kasumigaseki building in Tokyo, the first skyscraper in Japan.

“I wanted to contribute in one way or another to society through creating something new and unique,” he recalls. “I wanted to construct something huge, beautiful, deep inside the sea or on the moon.”

He majored in structural engineering as an undergraduate, but it was his bachelor’s thesis that provided the window to seismology.

“When I chose the theme of my thesis, I chose the soil-structure interaction problem rather than the structural mechanics or design of buildings,” he says.

This led Kawase to studying ground motion, which became one of the central focuses of his career.

After receiving his master’s degree in 1980, Kawase began working as a researcher in the atomic power department at Shimizu Corporation, one of the world’s premier architecture and engineering firms.

“In Japan, most of the major construction companies have their own research institutes for specific needs,” says Kawase. “I spent my time investigating ground motions to know how their characteristics are created and better be able to predict them.”

Kawase and his colleagues would provide this information to engineers, who would factor their research into design guidelines for important structures such as nuclear power plants, high voltage electrical towers and high-rise buildings.

Yet the relationship between seismology and engineering isn’t as close as Kawase would like it to be. While new research is being done, it doesn’t always find its way into broader building codes, he says.

“Seismology is influencing engineering in a very indirect way – through the actual earthquake disasters themselves,” he notes. “Japanese structures are relatively strong because they have been frequently suffering from strong ground motions in the past. It’s an example of survival of the fittest. But this doesn’t guarantee that the collaboration and communication between engineers and seismologists in Japan is ideal.”

It’s a problem that Kawase hopes to overcome. When he’s not in the classroom or office, he’s in the field, where he brings together his engineering and seismology expertise.

A major part of his field work is centered on measuring microtremors – the low-amplitude, often unfelt shaking that’s always occurring on the Earth’s surface. This shaking can be caused naturally by wind or ocean waves crashing on a beach. It can also come from heavy machinery and motor vehicles.

Preparing for a field measurement in Algostoli, Greece

While they don’t appear very large on seismograms, microtremors can tell researchers a lot about the ground in a particular area, particularly how it might react during an earthquake. For Kawase, these measurements help “create a theoretical model that calculates the responses of both ground and structure to the predicted seismic input.”

It’s the focal point of a project he’s currently working on with Cecile Cornou of ISTerre and Alan Yong of the U.S. Geological Survey. By evaluating the frequencies of microtremors, they’re hoping to improve predictions of site amplification characteristics – basically, how the makeup of the soil itself amplifies earthquake shaking.

“The next step is to check the applicability of our proposed method under different geological and tectonic conditions around the world,” Kawase says. “My hope is that we can provide region-specific mapping functions for better prediction of site amplification factors.”

His other fieldwork consists of conducting shaking table and pull-down tests, two methods of testing the vulnerability of structural elements like retaining walls or wood buildings during earthquakes.

Kawase’s work extends beyond Japan. He’s collaborating with Arben Pitarka of the Lawrence Livermore National Laboratory and Luis Dalguer, a consultant in Switzerland, to improve how earthquakes – and their sources – are modeled.

To do this, they’re attempting to simulate the dynamic rupture propagation on a fault in order to generate realistic seismograms that offer insights into how that fault will act in future earthquakes.

These seismograms are so far only capable of being produced via kinematic source representation – a way of describing things like fault slip that doesn’t consider the stress conditions causing the slip.

“These representations are not necessarily physical,” he says. “For example, the stress in a kinematic representation can be infinite at some positions, which is impossible in the real world. I hope that dynamic rupture models will produce realistic yet physically plausible slip evolutions.”

His childhood ambitions of building something unique are still a part of him. They’re just focused underground now.

“If I had a billion dollars to spend on seismology,” Kawase says, “I’d build a laboratory 10 kilometers below the surface, across a major fault like the San Andreas in the United States or the Median Tectonic Line in Japan and initiate real earthquakes there under a controlled environment.”

“We may need to buy an insurance policy, though” he jokes, “in case one of those earthquakes triggers the ‘big one.’”

SSA At Work is a monthly column that follows the careers of SSA members. For the full list of issues, head to our At Work page.